[PATCH 3.16.y-ckt 021/130] ipr: Fix incorrect trace indexing

[Luis Henriques]

3.16.7-ckt17 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Brian King <brking@xxxxxxxxxxxxxxxxxx>

commit bb7c54339e6a10ecce5c4961adf5e75b3cf0af30 upstream.

When ipr's internal driver trace was changed to an atomic, a signed/unsigned
bug slipped in which results in us indexing backwards in our memory buffer
writing on memory that does not belong to us. This patch fixes this by removing
the modulo and instead just mask off the low bits.

Tested-by: Wen Xiong <wenxiong@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Wen Xiong <wenxiong@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: James Bottomley <JBottomley@xxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 drivers/scsi/ipr.c | 5 +++--
 drivers/scsi/ipr.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index debc569ab26c..2f49d7b01485 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -592,9 +592,10 @@ static void ipr_trc_hook(struct ipr_cmnd *ipr_cmd,
 {
 	struct ipr_trace_entry *trace_entry;
 	struct ipr_ioa_cfg *ioa_cfg = ipr_cmd->ioa_cfg;
+	unsigned int trace_index;
 
-	trace_entry = &ioa_cfg->trace[atomic_add_return
-			(1, &ioa_cfg->trace_index)%IPR_NUM_TRACE_ENTRIES];
+	trace_index = atomic_add_return(1, &ioa_cfg->trace_index) & IPR_TRACE_INDEX_MASK;
+	trace_entry = &ioa_cfg->trace[trace_index];
 	trace_entry->time = jiffies;
 	trace_entry->op_code = ipr_cmd->ioarcb.cmd_pkt.cdb[0];
 	trace_entry->type = type;
diff --git a/drivers/scsi/ipr.h b/drivers/scsi/ipr.h
index b22b23586f93..2459391105fc 100644
--- a/drivers/scsi/ipr.h
+++ b/drivers/scsi/ipr.h
@@ -1480,6 +1480,7 @@ struct ipr_ioa_cfg {
 
 #define IPR_NUM_TRACE_INDEX_BITS	8
 #define IPR_NUM_TRACE_ENTRIES		(1 << IPR_NUM_TRACE_INDEX_BITS)
+#define IPR_TRACE_INDEX_MASK		(IPR_NUM_TRACE_ENTRIES - 1)
 #define IPR_TRACE_SIZE	(sizeof(struct ipr_trace_entry) * IPR_NUM_TRACE_ENTRIES)
 	char trace_start[8];
 #define IPR_TRACE_START_LABEL			"trace"
--
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